1. Field of the Invention
The present invention relates to a color cathode ray tube, and in particular to a color cathode ray tube which is capable of lowering a stress occurred due to an internal vacuum pressure of a cathode ray tube by optimizing a structure of a funnel yoke portion.
2. Description of the Prior Art
As depicted in FIG. 1, the conventional color cathode ray tube includes a panel 10 in which a R, G, B fluorescent surface 40 is coated onto the internal surface and an explosion proof means is fixed to the front surface portion, a funnel 20 welded to the rear end of the panel 10, an electron gun 130 inserted into a neck portion 140 of the funnel 20 and radiating an electron beam 60, a deflection yoke 50 deflecting the electron beam 60, a shadow mask 70 installed inside the panel 10 with a certain interval and having a plurality of holes so as to pass the electron beam 60, a main frame 30 and a sub frame 35 fixedly-supporting the shadow mask 70 in order to make the shadow mask 70 maintain a certain distance from the internal surface of the panel 10, a spring 80 for connecting-supporting the frame and panel 30, an inner shield 90 shielding the cathode ray tube against the external earth magnetic field and a reinforcing band 110 installed to the side circumferences of the panel 10 in order to prevent external impacts.
And, a CPM (convergence purity magnet) 100 for adjusting a proceeding trajectory of the electron beam 60 so as to make it land on a target fluorescent accurately is included in order to prevent a color purity defect.
A general fabrication process of the conventional color cathode ray tube can be divided into the first half process and the latter half process, the first half process is coating a fluorescent surface onto the internal surfaces of the panel 10, and the latter half process consists of below several processes.
First, in a sealing process, the panel 10 in which the fluorescent surface is coated and includes a mask assembly is joined to the funnel 20 in which frit is coated onto the sealing surface. After that, in an enclosing process, the electron gun 130 is inserted into the neck portion 140 of the funnel 20. And, in an exhausting process the cathode ray tube is sealed after vacuumizing internal space of the cathode ray tube.
Herein, when the cathode ray tube is in the vacuum state, a high tensile force and a high compressive stress act on the panel 10 and the funnel 20.
Accordingly, after the exhausting process, in order to disperse the high stress acting on the front surface of the panel 10, a reinforcing process for adhering the reinforcing band 100 is performed.
Recently, with digitalization, a cathode ray tube has been slimmed down by reducing the total length.
In more detail, the less the total length of a glass of the panel 10, the more a volume of the cathode ray tube decreases. However, a vacuum quantity is constant, accordingly the less the volume of the cathode ray tube, the more stress acts on the glass.
In addition, when the total length of the cathode ray tube is reduced, because a high stress acts on the funnel 20 having a thinner thickness than that of the panel 10, particularly a high tensile stress acts on a seal line portion at which the panel 10 and the funnel are joined, the color cathode ray tube may easily damaged in a thermal process.
In more detail, as depicted in FIG. 2, the total length of the cathode ray tube can be reduced by reducing the total length of the panel 10 or reducing the total length of a body portion 160.
However, when the total length of the panel 10 is reduced, because a high tensile stress occurs on the seal line portion due to vacuum after the exhausting process and a width of the reinforcing band 110 is limited due to decrease of a space for combining it, accordingly a stress disperse effect is reduced.
FIG. 3 illustrates a distribution of stress acting on the panel 10 and the funnel 20 when the inside the cathode ray tube is in the vacuum state after the exhausting process, a dotted line describes a compressive stress, and a tensile stress describes a tensile stress.
When the glass in which the panel 10 and the funnel 20 are combined a receives an external impact and a crack occurs. Herein, the tensile stress applied to the glass surface accelerates proceeding of the crack, the glass may be totally broken in the worst case.
On the contrary, the compressive stress prevents proceeding of a crack.
In more detail, as depicted in FIG. 3, because the compressive stress acts on the central portion 11 of the panel 10, the skirt central portion 12 and the central portion 21 of the funnel 20, they are relatively strong to impacts. However, because the tensile stress acts on the corner portion of the panel 10 and the seal line portion 14, they are sensitive to impacts.
In addition, as depicted in FIG. 4, the compressive stress acts on a long side 151 and a short side 152 of the funnel yoke portion 150. On the contrary, the tensile stress acts on the corner portion 153, it can be damaged by a weak impact.
Accordingly, in design of the glass, the tensile stress has to be sufficiently considered, in the conventional art, a limit stress value of the glass is not greater than 12 MPa.
Herein, in the funnel body portion 160, a stress can be efficiently lowered by using a certain ratio in fabrication of its shape or increasing a thickness locally. However, in the yoke portion 150, when a general shape in FIG. 4 is applied, a tensile stress of 15˜20 MPa in FIG. 5 acts on, it is impossible to reduce the stress efficiently with a glass having a limit stress value as 12 MPa. In addition, because a high stress occurs, there are lots of difficulties in fabrication processes.
In addition, in order to secure an impact resistance of the glass, a reinforced glass having an improved physical strength at its surface by performing a thermal process besides installing the reinforcing band 110 is used or a film is coated onto the surface of the panel 10, etc.
However, all the above-described methods are for the panel 10, in the funnel 20, it has little effect in a reinforcing band installation, and in general the funnel 20 does not use a reinforced glass passing a reinforcing thermal process as its material.
In addition, when a glass thickness of the funnel yoke portion 150 increases, a tensile stress on the portion decreases, however a shade occurs on the screen at which the fluorescent surface 40 is coated when the electron beam 60 hits the internal surface of the yoke portion 150, there is limitation to increase a glass thickness.
Accordingly, mechanical techniques capable of securing an impact resistance and lowering a stress on the yoke portion 150 of the funnel 20 are required.